1. Field of the Invention
The present invention relates to an internal combustion engine fuel pressure control apparatus, and in particular to an internal combustion engine fuel pressure control apparatus suited for controlling the pressure of fuel supplied to a fuel injection valve in a cylinder fuel injection type internal combustion engine.
2. Description of the Related Art
In cylinder fuel injection type internal combustion engines, an accumulator fuel injection control apparatus is usually used. Namely, the accumulator fuel injection control apparatus comprises: an accumulation chamber that accumulates fuel in a high-pressure state; a high-pressure fuel pump that sucks in fuel and discharges the fuel to the accumulation chamber; an injector that injects/supplies the high-pressure fuel accumulated in the accumulation chamber to cylinders of the internal combustion engine; and control means that controls the injection period and injection quantity of the fuel and the discharge quantity of the high-pressure fuel pump. The high-pressure fuel pump comprises: a cylinder; a pump piston that is driven by a pump drive-use cam disposed on a rotating shaft (e.g., a cam shaft) of the internal combustion engine, pumps inside the cylinder, sucks fuel into a booster chamber during the suction process and discharges the fuel inside the booster chamber to the accumulation chamber during the discharge process by a reciprocating motion in the cylinder and a spill valve that relieves the fuel boosted inside the booster chamber to a low pressure at a predetermined timing to control the discharge quantity from the booster chamber to the accumulation chamber and control the fuel pressure of the accumulation chamber to a predetermined pressure.
The fuel discharge quantity from the booster chamber to the accumulation chamber is determined by the feedforward quantity corresponding to the same quantity of fuel as the fuel supply from the injector to the cylinders and the feedback quantity calculated by known PID control that conducts a proportional, integral and differential operation on the basis of the deviation between the target value and the actual measured value, and the timing for driving the spill valve is determined on the basis of the determined fuel discharge quantity and the running condition (e.g., see Japanese Patent No. 2,890,898).
In such an accumulator fuel injection control apparatus, there is the problem that the fuel injection quantity fluctuates due to changes over time in the discharge efficiency of the fuel pump, differences in the airframe of the fuel pump, or differences in the capacity of the fuel pipe system. With respect to this problem, Japanese Patent No. 3,136,938 discloses taking the following countermeasure.
Namely, in a known fuel pressure control apparatus that conducts a proportional, integral, and differential (PID) operation on the difference between the target fuel pressure and the measured fuel pressure to control the discharge quantity of the fuel pump, learning means is disposed which, when the integral term of the PID operation deviates from a predetermined range, executes learning that changes the proportionality constant used in the PID operation and adjusts the integral term to fall within the predetermined range.
Also, in a known fuel pressure control apparatus that conducts a feedforward operation so as to maintain the fuel pressure at a target fuel pressure by supplying, to a fuel accumulation chamber and with a fuel pump, the same quantity of fuel as the fuel quantity supplied from the fuel injection valve to the cylinders, control quantity determining means is disposed which multiplies a correction coefficient with the fuel quantity to be supplied to the fuel accumulation chamber to determine the fuel quantity that the fuel pump is to discharge, and which conducts integral correction to determine a control quantity for controlling the discharge quantity of the fuel pump, and learning means is disposed which, when the integral correction fuel quantity deviates from a predetermined range, executes learning that changes the correction coefficient and adjusts the integral term to fall within the predetermined range.
As described above, because it is necessary to control the spill valve at a predetermined timing in response to the life of the pump drive-use cam, the spill valve is controlled using a rotary signal to indicate the position of the pump drive-use cam. As disclosed in Japanese Patent No. 2836282, for example, there are apparatus that use the signal of a crank angle rotary sensor as the rotary signal. In this case, because the installation error between the pump drive-use cam and the crankshaft becomes a problem, the installation error is compensated by the phase difference between the signal of the cam angle rotary sensor to which the pump drive-use cam is attached and the signal of the crank angle rotary sensor.
However, it is difficult for the fuel pressure control apparatus disclosed in Japanese Patent No. 3,136,938 to accurately compensate both fluctuations in the fuel injection quantity resulting from changes over time in the discharge quantity of the fuel pump, differences in the airframe of the fuel pump, or differences in the capacity of the fuel pipe system, i.e., fluctuations and variations stemming from the discharge quantity of the fuel pump, and fluctuations and variations that affect the drive timing of the spill valve, such as the output tolerance of the cam angle rotary sensor, the manufacturing tolerance of the plate engine, and the installation error between the fuel pump and the pump drive cam with respect to the rotary signal.
More specifically, the fuel pressure control apparatus disclosed in Japanese Patent No. 3,136,938 executes learning which changes the proportionality constant used in the PID operation when the integral term of the PID operation deviates from the predetermined range, and the operational quantity is one of either the discharge quantity or the drive timing. Namely, to describe a specific example assuming that the operational quantity of the fuel pressure control apparatus disclosed in Japanese Patent No. 3,136,938 is the drive timing, fluctuations and variations that affect the drive timing of the spill valve are corrected by an integral term within the predetermined range, and fluctuations and variations stemming from the discharge quantity of the fuel pump are corrected by learning that changes the proportionality constant. However, because the operational quantity that is the result of the PID operation is the drive timing of the spill valve, when the running point has changed from the point where learning that changes the proportionality constant was conducted, it is difficult to accurately compensate fluctuations and variations stemming from the discharge quantity of the fuel pump. As shown in FIG. 11, for example, this is because the discharge quantity and the drive timing usually have a nonlinear relationship.
In the system disclosed in Japanese Patent No. 2,836,282, the phase difference between the signal of the cam angle rotary sensor and the signal of the crank angle rotary sensor is simply detected. Thus, the installation error between the pump drive-use cam and the crankshaft can be compensated, but the installation error between the fuel pump and the pump drive cam with respect to the rotary sensor cannot be corrected, and there is the concern of error arising in the discharge fuel quantity.
When error arises in the discharge fuel quantity, the fuel pressure inside the accumulation chamber is no longer controlled to the predetermined pressure. Thus, there is the potential for the fuel injected from the fuel injection valve to depart from the optimum condition and for the intended air-fuel mixture to not be obtainable. As a result, the combustion of the internal combustion engine deteriorates, and there is the concern of the runability and exhaust gas of the automobile to deteriorate.